Manganese(II) ethylenebis(dithiocarbamate) (maneb) is an important fungicide. The compound, however, is unstable and will tend to decompose, particularly at elevated temperatures.
Decomposition products, such as ethylenethiourea (ETU), can be found in freshly made maneb, and their concentrations will increase during storage. Although much work has been done to improve the stability and fungicidal activity of maneb, there are no known references which teach a method for reducing the ETU content of maneb.
L. Donev [Khimiyai industriya (Sofia) 41, 100-101 (1969), No. 3], for example, teaches a method of preparing maneb of increased dithiocarbamate content in which aqueous formaldehyde is added to a manganese(II) sulfate solution. Then a solution of ammonium ethylenebis(dithiocarbamate) (amobam) is added to precipitate the maneb. ETU concentration is not discussed.
U.S. Pat. No. 3,856,836 discloses a maneb derived from a formaldehyde-treated reaction mixture. The maneb is precipitated in aqueous medium from a water-soluble salt of ethylenebis(dithiocarbamic acid) and a water-soluble manganese(II) salt. Formaldehyde is added to the reaction mixture after precipitation. The reference does not discuss ETU concentration.